In an image forming apparatus such as a copying machine, a heater is used to fix a toner that is adhered to a medium such as a recording sheet. In such a heater, for example, a ceramic substrate is provided with a heating resistor. In a manufacturing process of a heater, groove lines (split line) are formed on a flat plate-shaped base material through groove processing using a laser scribing technique and the base material is split into a plurality of heaters along the groove lines thereby manufacturing heaters with desired external dimensions.
As one of methods of increasing the thermal efficiency of a heater, there is a method of decreasing the thickness of a substrate. Particularly, in a case of a ceramic substrate, as the thickness of the substrate decreases, micro cracking starting from a groove portion, which is split along a groove line, becomes more likely to occur while causing a decrease in mechanical strength and thermal shock strength of the substrate. Therefore, a technique of suppressing a decrease in mechanical strength of the substrate by forming a glass film on an end surface of the substrate is known.
However, the above-described manufacturing process of a heater has a problem that the productivity of a heater decreases since a processing process of forming a glass film on an end surface of a substrate after a base material is split into a plurality of heaters, is added.
Therefore, an object of an exemplary embodiment is to provide a heater, an image forming apparatus, and a manufacturing method of a heater with which it is possible to suppress a variation in external dimension of a substrate and to suppress a decrease in mechanical strength and thermal strength of the substrate without adding a processing process.